Apparatus for the manufacture of sulfuric acid



July 18, 1950 w. s. ALLEN APPARATUS FOR THE MANUFACTURE 0F SULFURIC ACID Flefi Oct. 30. 1946 vATTORNEY.

9 0 M H It. 2

Patented July 18, 1950 APPARATUS FOR THE MANUFACTRE'OF sULFURIc ACID ,y

Waiter s. A11en,F1ushing,N. Y., assignor to Allied Chemical & Dye Corporation, a corporation of y New York y Application October 30, 1946, Serial No; 706,755` ,i I

This invention relates to processes for making so-called chemically pure sulfuric acid, and also to apparatus suitable for use in the manufacture of such acid.

One of the common methods for making C. P. (chemically pure) sulfuric acid is by absorption of the sulfur trioxide exit gas of a catalytic oxidation contact process in water or dilute sulfuric acid under suitable conditions to produce C. P. sulfuric acid. Also, it is known to mix contact process sulfur trioxide with steam to form sulfuric acid vapor which is then condensed to form C. P. sulfuric acid.

While prior methods for making C. P. sulfuric acid result in production of acid of relatively acceptable quality, trade specification requirements are constantly becoming more rigid. Further, the use of spent oxide and flotation concentrate pyrites as sulfur-bearing raw materials in the contact process gives sulfur dioxide gases emanating from the burners carrying small amounts of nitrogen compounds asA impurities which subsequently appear in the sulfur trioxide gas leaving the converter system. If converter exit gases of this type are used as such for manufacture of C. P. acid, the nitrogen impurities contaminate the acid product.

One object of my invention is accordingly to afford improved inexpensive processes and apparatusv for making sulfuric acid of high purity. Another object vis to provide process features which eliminate the above-noted nitrogen com pound contaminating conditions. v

Other objects and advantages will appear as the description of my invention proceeds.

In accordance with a preferred embodiment of Amy invention, I have found that high quality sulfuric acid may be made by procedure comprising introducing steam and gaseous substantially pure sulfur trioxide containing substantially no nitrogen compounds into the upper end of a relatively vertically disposed reaction zone and passing said steam and sulfur trioxide downwardly thru said reaction zone whereby sulfuric acidy vapor is formed, passing the resulting sul.- furic acid vapor upwardly-thru a. substantially vertically disposed condensing zone, cooling said vapor in said condensing zone to-liquefy` sulfuric acid, said zones, beyond the point `of initiation of the sOa-HzO reaction, being formed by an integrally fabricated, unbroken, continuous wall of acid-resistant material, collecting. sulfuric acid in a sump section formed by saidwall and disposed at the bottoms of and lyingintermediate said zones, and withdrawing chemically pure sulfuric acid from said sump section.

4 Claims. (Cl. 212,' 26515v 'l l,

Inthelaccompanyingdrawing, Fig. 1'. is a lvertical sectional view showingone form vof apparatus particularly adapted for use in the practice of my processand Fig. 2 is a horizontal sectional View of a detail of this apparatus taken on line 2--2 of Fig. 1.

Asv shown in Fig. 1 of the drawing, I designates a U-shaped tube formed by an integrally fabricated, unbroken, continuouswall of acid-resistant material such as fused and molded silica and having a short arm 2, a long arm 3, and a U-bend 4 therebetween. Mounted in shortarm 2 by any suitable means is a steam inlet tube 5 having an opening Withinand somewhat below the top of short arm 2. Suspended thru a plate 6 lat the top of long arm 3 is an internal bayonet-type cooler comprising an elongated tube 1 of acid-resistant material, preferably silica, supported on plate 6 by a thicknessof packing 8 placed about the upper portion of tube 1 extending above plate 6. Tube 1 has mounted therein cooling water inlet tube 9 and water outlet tube IU, the two latter tubes being inserted into tube 1 thru a collar II fastened to the top of tube 1 by any suitable means. In the upper portion of long arm 3 near its top is a residual gas outlet I2 forming an integral part of U,shaped tube I. The bottom of the U-bend 4 forms a sump section I3 terminating at its lowermost portion in a liquid outlet I3'. Attached to short arm- 2 yof U-shaped tube I by means of a single packed joint I4 is an inverted U-shaped gas` inlet pipe I5 made of suitablematerial such as silica. The other end of gas inlet member I5 extends a short distance into the top of a gas filter receptacle I6 containing packing material I1, such as pebbles, said packing being supported by a perforated plate I8 at the bottom of receptacle I6. Receptacle I6 is directly connected by means` of inclined members I9 to a pipe 20 connected preferably to. an oleum still not shown. Vertical pipe section 2B may be connected to a suitable liquid seal not shown.

Secured to the outer walls of long condensing arm 3 by any suitable means are metallic conically shaped members 2|, 22,*23 and 24. Fig. 2 more clearly shows the structure of each of these members as represented by. member'2l having a number of approximately equally spaced small holes 29 about its lower inner circumference as water outlets. These members serve to direct auxiliary cooling water, if necessary, in streams down the outer walls of long condensing arm 1 in a manner to be hereafter described. I

My device in its ypreferred embodiment comprises a U-shaped tube having a short arm 2 forming a reaction zone and a long arm 3 aording a condensing zone. A longer arm is provided for the condensing Zone as compared to the arm housing the reaction zone in order to afford sufficient coolingsurface, as provided by the outer wall of a long'bayonet-type cooling "tube 1 and the inner wall of long arm 3, to promote a gradual rather than a sudden condensation of the. sulfuric acid vapor for reasons later to be noted.' However, if desired, both armsr may. be; `constructed of equal length if sufficient surface kisprovided in the condensing arm to=resultin the above-noted gradual cooling eflect.Y

U-shaped tube I and the bayonet-type cooling tube 1 have been specified as constructed of an acid-resistant material such as fusedlandmolded silica. It is to be further noted in this connection that all other parts'of my apparatus presenting surfaces in contactwith .sulfuric..acid

vaporl or liquid sulfuricacid'are. also ,fabricated preferably .of the. same yacid-.resistant material; The constructionof"U-sliapedtuba.l in the form of. an .integrally fabricated',r unbroken,r continuous wall of acid-resistant materialliavingonly.

onel ypacked jointis.,animportantiatiire `of my invention.r As .themesult offsllch structure, l.nonvolatile contaminating material from seepage thru the joint'packing, usuallymade .of asbestos and sodium silicate, .isliiept .at a minimum, kespecially since the arrangement ofStructural"elementsis.

suchv that the SOs-Hzolreaction 'is initiated .within.. the. U-shapedtllbfe I"'jat @a point beyond. the packed-joint |4,.i. e, .theyicinity ofthe inner end .ofsteam inletV pipe 5."

Asl described in greater .detail in rrelation to the aboveY apparatus, my processis .carried out'in the following manner: Y Sulfur. trioxide'gassubstantially free from contamination lby nitrogen compounds is first .passedaaelevatedtemperature thru piping Iinto the'lowerportion ofreceptacle;

l 6, thence thru .perforatedplate ,1 8 "'andupwardly.

Steam is introduced*intdtliiszonethrul steam inlet tube 5 and is mixedwith tl'iepsulfurtrioxide v gas to form sulfuricacid'vapor The resulting sulfuric acid vapor is then `conducted th-ru .IJ-bend 4 into' the condensingzone in'long'arlntwhere the .sulfuric acid vaporpcomes Linto contact with the cool inner wall oflongarm 3f and-with the The 'hot' 'purified sulfur triouter wall of the bayonet-type coolingtube 1,v

keptcool by the' circulation of Waiter-therethruby means of waterinletiand outlettu'bes 9' and lc, respectively. Condensation of sulfuric acid vapor then takes place andthe condensed droplets of sulfuric acid' runV down' the outer wallof the bayonetk cooling tube .,'ffand theiinner 'wall off'long arm 3 :andare discharged; thru the sump' section I3 andliquid'outlet |'3' in4v the l'owermostportion of U-bendd. The discharged C. P. sulfuric .acidA is then passed to` an acidfsea'l, a cooler', and finally to storage, all not shown: Any Yresidual uncondensed gas passesj thru; outlet I2 in` the4 upper portion of long arm'andisjconducted to-any suitable scrubber such 'as'a coke box, not shown.

As above indicatedj whenY sulfur- -dioxic'ie gas .is prepared from' Athe presentwidelyusednely divided sulfide ores, thisgas-contains'small amounts eoA of nitrogen compounds which appear in the form of traces of nitric acid or nitrosyl-sulfuric acid in the sulfur trioxide leaving the converters of the well-known contact process, and carry on thru to contaminate the sulfuric acid product. Under these. circumstances, in the manufacture of C. P. sulfuric acid it is thus necessary to treat contact sulfur trioxide gas or the finis-hed sulfuric acid product with a regulated amount of hydrogen `sul'de' todestroy these nitrogen compounds, and .the-.sulfur dioxide formed vfrom this reaction is difficult to remove.

In ,the practice of the present improvements,

'the foregoingdifculties are overcome by using,

as a source of sulfur trioxide, a sulfur trioxide gas formedbyffdistillation of oleum. According to the invention, it has been found that when oleum containing nitrogen compound contaminants is distilled, such contaminants remain as still bottoms and therejis forni-cdaW sulfurtri'oxidegas which-r contains substantially no deleterious nitrogen compounds. Thus, an important feature of my process is provision of a'sulfurtrioxide gasv substantially freed ofcontaminating nitrogen compoundsg'andl find that such agas maybe obtained v`read-ily bythe distillationof commercial oleum'whi'clirmaybe made by the ordinary known processes land' which, particularly when produced from `SO2 gases 'formed 'by combustion of sulflde's; isvusua-lly contaminated with nitrogen compounds;

The oleum employedmay be othe lcustomary commercial strengths,I e. g. 20-'65%. Preferably,v distillation of oleumis leffected by external heatingto temperatures sufficiently high towaporize S03 but not highenougliv to boil off yany sulfuric acidvapor.V Byu suchprocedure, therel is formed an S03y gaswhichiis not only substantially free from contaminating; nitrogen compounds but is Ialso substantially-pure in other respects'iand for practical purposes maybe considered Vas S03. However, with' respectto the Vsulfur trioXide gas usedfin-c'arrying out "the instantprocess, apartffrom substantial absence of contaminating Ynitrogen4 compounds; it' vris not Wholly essential that the sulfurrtriox'id Jgasv be otherwise substantiallypure. Thus, it isf possible to employ an S03 gas which may contain some appreciable vquantities. of' inert diluents, such as air, although inl reasonablygood practice of the invention, it ispreferred to use -a ysulfur trioxide gas of strengthlnot less than'about' 90% S03.

The particular'l sulfuntrioxide gas employed is conducted at temperature ofaboutZOO Fi into short arm 2 into which steam issimultaneously charged in regulated'proportions. Reaction of S03 and steam to form sulfuric acid vapor takes place substantially instantaneously atfthe point of introduction of steam iritothe sulfur trioxide gas and substantial quantities'ofr heatfare `eren'- erated, such heat comprising hea-t, ofthe 30s-H2O reaction andheat off'dilution'of sulfuric acid. If union of sulfur trioxide andsteam takesl place at a temperature below the devvr point of the resulting sulfuric ,acidfvapon' sulfuric acid mist forms. Particularly in the presence ofappreciable quantities of inert` carrying gas; .this mist cannot be condensed Vina simple condensing system but is carried along; thru thecondenser in suspension in the gas .stream causing an eco'- nomic loss and a nuisance. When-the ordinary relatively dilute S03 exit gas ofa catalytic converter system is employed inthe reactionjwith. steam, it may be necessaryto` addexternal heat to the heat of reaction produced by union-of S03 and steam to raise this large body of gas' a gas which has an S03 concentrationpreferably` not less thanv 90%, and by regulating the quantity of steam introduced thru inlet 5 so that the sulfuric acid formed and eventually'collected in siunp I3 has an H2SO4 strength of not less than 80%. I find that by so 'controlling'the S03 strength ofthe incoming 4gas and limiting the quantity of steam utilized as indicated, there is always generated in the Vreactionzone in short arm 2 adequate quantities of heat to maintain temperatures wellabove the dew pointfof the sulfuric acid being produced, thus avoiding the formation of sulfuric acid mist.

In the practice of better embodiments of the invention, it is preferred to operate in suchfa way that the liquid sulfuric acid collecting 'insump I3 and draining out of the apparatus thru outlet I3' has a temperature of not less than 300 F. At this high temperature of acid discharge, any sulfur dioxide gas incidentally and unavoidably present in the system is vaporized out of the liq uid sulfuric acid and is eventually discharged from the apparatus thru outletpipe I`2. `This condition results in production of C. P.-sulfuric acid of very low SO2 content. l In order to maintain the indicated 300 F. temperature in the liquid acid discharged thru outlet I3', I `find that it is preferable to so restrict the quantity of steam introduced thru inlet 5 as to maintain temperatures in the vicinity of the outlet end of pipe 5 not less than about 400 F. In turn, such temperatures of 400 F. and higher may be created readily by controlling introduction of steam so that the resulting liquid sulfuric acid condensate has an H2504 strength of at least 80%, that is by adjusting the quantity of steam introduced so that the strength of the liquid product of the process is about 80% I-IzSOi and upwards, temperatures of 400 F. or more are automatically maintained in the SC3-H2O reaction zone in short arm 2.

The sulfuric acid vapor formed in short arm 2 is conducted around U-bend 4 and thence upwardly into long arm 3 of U-shaped tube I, where it is condensed under conditions avoiding sudden cooling or chilling of the vapor so as to again restrain formation of sulfuric acid mist. To carry out this purpose, condensing arm 3 and the bayonet-type cooling tube 1 are each preferably constructed so as to provide a condensing zone about three times the length ofv steam inlet arm 2. This feature of construction provides substantial cooling surface to bring about a gradual cooling of the sulfuric acid vapor and its condensation in droplets on the inner wall of long arm 3 and the outer wall of bayonet cooler tube 1.

If it is desired to obtain a greater cooling effect than that produced by bayonet cooler tube 1 alone, especially on warm days, water may be poured into the uppermost conically shaped member 2I as shown by arrow 25. The water drains out of the bottom of member 2l thru holes 29 in the lower portion thereof and continues to flow down long arm 3 and into the next lowest conical member 22. In this manner, a stream of water is kept continually flowing about the outer wall of a considerable portion of the length of long arm 3 and finally is conducted to a sewer outlet (not shown) after its lpassage thru the holes 29 inthe lowestconical member 24. A

larger quantity of Water may be furnished for this purpose by also introducing water directly into the top of conical members 22, 23 and 24, as

shown by arrows 26, 21 and 28, respectively.

My U-shaped tube may also be employed with equal facility as a condenser in a process wherein commercial sulfuric acid is distilled over to make sulfuric acid of C. P. quality. Further, it may be utilized as a simple condenser for other acids, e. g. nitric or hydrochloric, to obtain a chemically pure product. steam inlet means is required in the short arm t2 of U-shaped tube I. I

least and anywhere in the range of 80l00,%

strength and of high 'purity may be recovered. For example, using as a source of S03 a commercial oleum containing about 0.0001%` by weight of nitrogen impurities as HNOa, by practicefof the process in the apparatus described,v itl is possible to make a -100% sulfuric acid product containing less than 0;00001% Fe, 0.0003% SO2, 0.0001% non-volatile'matter, and 0.00002% nitrogen impurities as HNOS. Thus, contamination by nitrogen compounds, sulfur dioxide, and non-volatile material from seepage thru packings of joints in condenser equipment is minimized. Further, by reason of use of strong S03 gas and other features of the invention, practically all the constituents pre-sent are condensed and practice shows that, when using S03 gas, the condenser tail `gas losses amount to less than 0.25% by weightoftotal production. Further, gas pressures within the apparatus are minimized, and no leakage problems are presented.

If desired, a section in the condensing arm 3 below the cooler-1 and a portion of the lower annulus between cooler 1 and the adjacent inner wall of arm 3 may be provided with packing material, e. g. suitable pebbles or rings. When so arranged, this feature of the invention may be utilized to produce C. P. oleum of e. g. 30% strength.

Certain process aspects of the disclosure of this application are included in the claimed subject matter of my copending application Serial No. 794,034, filed December 26, 194'1.`

I claim:

1. Apparatus of the character described comprising a tube having a pair of vertically disposed arms and a connecting upwardly formed U-bend therebetween, means for introducing a reactant into the end of one of said arms, means for introducing a second reactant into said arm adjacent said end hereof, heat transfer means disposed internally in the other arm, means for supplying heat transfer medium to said transfer means, a reaction product outlet adjacent the top of said other arm, a reaction product outlet at the lower portion of said U-bend, said tube in its entirety being unitary, jointless, and formed by an integrally fabricated, unbroken, continuous wall of acid-resistant material.

2. Apparatus of the character described comprising a tube having a pair of vertically disposed arms and a connecting upwardly formed U-bend therebetween, means for introducing a reactant into the end of one of said arms, means for introducing a second reactant within said arm at a point substantially beyond said end of said arm, heat transfer means disposed internally in the other arm, means for supplying heat For each of these purposes, .no

transferinediumzto said` transfer mean-s, a reaction prductoutlet adjacent the top of :saidgother arm, az-i'ea'cti'ontproduct.outlet at the lower portion ofs'aidt U diend,7 said tube in its entirety being unita-ry, j'ointless, and formed by an integrally fabricated, unbroken, continuouswall of acidere'sistant material. l

3.- Appara'tus ofthe character described comprising a tube having a vertically disposed short arm. forming an. unobstructed reaction zone, a vertically disposed long arm forming an elongated heat transfer zone, and a connecting upwardly formed U-bend Vbetween said arms; ,means for introducing a reactantinto the end of .said short arm, means for introducing a second reactant within said short arm at a point substantially beyo'ndsai'd end of said "short arm, heattransfer means disposed internally and substantially throughout the length of `said long arm, means for supplyingy heat transfer medium to said transfer means, a reaction product outlet adjacent the topV o'f saidlong arm-y a reaction productv outlet at thelower portion of tsaid U-bend, said tube in its entirety being unitary, jointless, and formed by an integrally fabricated, unbroken, continuous wall 'of acid'resistant material.

4; Apparatus of the character described comprising atube having a vertically disposed short arm forming an unobstructed reaction; zone, a vertically disposed long arm forming an elongated cooling zone,` and a connecting upwardly formed U-bend between' said arms; means for introducing a reactant into the end ofsaid short arm, said means'comprising an inlet pipe at tached at one end-to vthe end of said short arm by means of a single joint; and a nlter associated withrthe-other end 'of said inlet pipe; means for introducing Aa; secondY reactant within l said short arm' atl aipoint substantially beyond said end of said'short-arm, a tubular silica heat transfer unit closed atits lower end and containing heat transfer medium inletia-nd outlet tubes at its top end,l said unit being disposed within saidlong arm and being suspended thru a plate at the tcp REFERENCES CITED Th'e following references are 'of record in thele of'ths patent:

UNITED STATES PATENTS y OTHER REFERENCES Ind. and Eng; Chem., Analytical ed., vol. 19, 1947, p. 144; 

1. APPARATUS OF THE CHARACTER DESCRIBED COMPRISING A TUBE HAVING A PAIR OF VERTICALLY DISPOSED ARMS AND A CONNECTING UPWARDLY FORMED U-BEND THEREBETWEEN, MEANS FOR INTRODUCING A REACTANT UNTO THE END OF ONE OF SAID ARMS, MEANS FOR INTRODUCING A SECOND REACTANT INTO SAID ARM ADJACENT SAID END HEREOF, HEAT TRANSFER MEANS DISPOSED INTERNALLY IN THE OTHER ARM, MEANS FOR SUPPLYING HEAT TRANSFER MEDIUM TO SAID TRANSFER 